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Morris says there's no immediate danger. It's a precaution in case winds change as some derailed cars continue to burn.

Morris estimates about 10 cars from a mile-long train caught fire and will have to burn out. She said it could take up to 12 hours before authorities can get close.

The derailment Monday afternoon happened about a mile outside of Casselton. The town of 2,400 people is about 25 miles west of Fargo.

Officials are still investigating what caused the derailment, but a second train carrying grain was somehow involved.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

A train carrying crude oil from North Dakota's oil patch derailed Monday near the small town of Casselton, setting off a series of fiery explosions. No injuries were initially reported, but officials were warning residents to stay indoors as the situation unfolded.

BNSF Railway spokeswoman Amy McBeth said a train carrying grain was first to derail, and it knocked several cars of the mile-long oil train off adjoining tracks. Several explosions were reported, she said.

Cass County Sheriff's Capt. Mitch Burris also told The Associated Press that the derailment appeared to result from the crude oil train striking a grain car, but he said investigators were still trying to determine exactly what happened.

Cass County Emergency Manager Dave Rogness said the town's 2,400 residents were told to stay indoors as a precaution.

Rogness said crews were calling for truckloads of sand to help contain leaking material. He says the derailment occurred near the city's ethanol plant.

Terry Johnson, the manager of a grain dealer less than a mile from the derailment, said he had heard at least six explosions in the two hours following the incident.

"Each one, you could hear the explosion," he said. "It shook our building and there was a huge fireball."

Johnson said he was staying inside his grain business, as directed by authorities, but could see the disaster through a window.

"The town is covered with black smoke," he said. "The wind is blowing a little, so the town doesn't have to breathe it."

State health officials were in Casselton and plan to check for health hazards once the fires are out, said Dave Glatt, director of the Health Department's environmental health section.

"We're just standing by waiting for emergency responders to get it under control," he said.

North Dakota is the No. 2 oil-producing state in the U.S., trailing only Texas, and a growing amount of that oil is being shipped by rail. The state's top oil regulator said earlier this month that he expected as much as 90 percent of North Dakota's oil would be carried by train in 2014, up from the current 60 percent.

That matches a growing national trend and has stoked fears of catastrophic derailments, especially in the wake of last summer's crash in Canada of a train carrying crude oil from North Dakota's Bakken oil patch. Forty-seven people died in the ensuing fire.

The number of crude oil carloads hauled by U.S. railroads surged from 10,840 in 2009 to a projected 400,000 this year.